1. Field of the Invention
The instant invention relates to a method and apparatus for characterizing a kerogen by measuring the variation, with time, of the fluorescent spectrum thereof. Both the spectral distribution and intensity at certain wave lengths change with the maturity of the kerogen.
2. Background of the Art
An important parameter to predict the potential for oil generation of a source rock is the alteration with time of the fluorescence emission during irradiation at a constant wave length as measured on a polished sample of such source rock. This parameter has been discussed by Teichmiller et al, Erdal v. Kohle, 30, pp. 387-398 and by Leythaeuser et al. Proc. 10th World Petrol. Congr. (Bucarest), 2, pp. 31-41, Heyden, London. Teichmiller reports that a positive alteration occurs in immature source rocks and a negative alteration occurs in mature source rocks when the fluoresence is measured at 546 nanometers. Thus, it is known that the measurement of alteration of fluorescence holds great promise in determining the level of maturity of organic matter within the sediment and its potential as a source of oil (hydrocarbons).
Conventional optical microscopic techniques cannot resolve and describe particles of kerogen smaller than about 1 micrometer. However, the characterization of the fluorescence of such small particles would yield important data as to maturity thereof. To this day, however, there is no microscope available which is suitable for providing the necessary data regarding the rapid decay or rapid change of the fluorescent spectra, with time, of such small samples of kerogen.
Various reported improvements in microscopes, that are used for purposes other than characterizing kerogen, have currently come to light. For example, in U.S. Pat. No. 4,329,015, a fiber optic cable is utilized to direct light into the microscope body to increase the amount of light available. The patentee reports that is necessary to tilt the objective lens of his microscope from the optical axis to ensure that spurious light or reflections from the surface of the objective lens do not appear in the visual plane of said microscope. It is clear that if reflectance is occurring, it would decrease to some extent the amount of light available at the eye piece of the microscope in relation to the amount of light provided by the fiber optic cable.
In U.S. Pat. No. 4,291,938, fiber optic cables are arranged around in an annular area coaxial with the optical axis of an imaging optical element. This arrangement arguably produces an improved dark field illumination in the microscope. It is noted that the patentee requires a curved objective lens to converge the light emanating from the ends of the optical fibers and thereby focus such light at the focal plane of the microscope. The shape of the lens disclosed in this patent is known to cause reflectance of at least a portion of the light which impinges thereon. Thus, again, the amount of light being provided by the fiber optic cables is greater than the amount available for illuminating a sample in the object plane of this microscope.
In U.S. Pat. No. 3,971,621, a microscope is described which utilizes, as a light conductor, a bundle of glass fibers arranged to provide light, at an angle of from 40.degree. to 50.degree., at the point at which the the optical axis intersects the objective of the microscope. Thus, this reference also discloses the use of a fiber optic cable in conjunction with a microscope; however, such use is to generate relief-like contrast of the microscopic images, only.
U.S. Pat. No. 4,120,565 discloses a microscope, for investigating the eye, which includes an optical guide in form of a glass element. The optical guide is illuminated at one end by a lamp and the radiation from the lamp is carried by the guide to provide uniform illumination around the eye that is being investigated.
Thus is clear that the use of fiber optics in the microscopes of the prior art have been limited to illumination from the well-known lamps of the prior art.
It is thus one object of this invention to provide a method of characterizing kerogens by analyzing the fluorescence thereof.
It is another object of this invention to provide a method of determining whether said kerogen is a hydrocarbon precursor by analysis of the fluorescence thereof.
It is another object of the invention to provide a system for analyzing the fluorescence spectrum of a kerogen.
Additional objects, advantages and features of the invention will become apparent to those skilled in the art from the following description.